The present invention relates to a dry surface cleaning apparatus using a laser; and, more particularly, to a dry surface cleaning apparatus using a laser with which a substrate may be cleaned without causing a surface damage regardless of types or sizes of surface contaminants with an enhanced cleaning speed and efficiency.
Contaminants such as micron and submicron sized particles on semiconductor surfaces can pose serious problems such as circuit failure and yield loss in a semiconductor device. For example, particles smaller than 0.06 micrometer can cause fatal device defects for a next generation dynamic random access memory and microprocessors. The contamination control on silicon wafers is therefore a crucial issue in the manufacturing thereof. More effective techniques to remove smaller and smaller particles from the surface are required as the density of chip devices keeps increasing. However, those small particles are more difficult to remove due to their higher adhesion force on the surface. Conventional cleaning techniques such as high pressure gas jet, scrubbing, ultrasonic and chemical flux are known to be ineffective in removing the small particles of micron or submicron dimensions and further, there is possibility for them to inflict a mechanical action-based damage in the surface profile as well as an environmental pollution problem due to the considerable water consumption and the use of chemicals.
Recently, a laser cleaning technique has been demonstrated to offer a new environment friendly approach for an effective removal of small particles, since it is a dry process. However, cleaning efficiency is strongly dependent on laser wavelength and physical properties of the particles since the removal of a small particle is closely related with a laser absorption property of the particle surface that produce a cleaning force, wherein a different particle surface produces a different cleaning force. Thus the removal of all particles having different optical and thermal properties by using a single wavelength is difficult due to the different interactions between laser and particles. In addition, cleaning speed is relatively slow due to the small laser spot sizes.
In order to tackle the problems in the conventional laser cleaning, Vaught, in U.S. Pat. No. 5,023,424, describes a shock wave particle removal method and apparatus using a laser induced shock wave to dislodge particles from a wafer surface. A laser beam is focused on a laser focus in the air by a lens so that the air around the laser focus may be ionized to generate a laser induced plasma shock wave and, therefore, the laser induced plasma shock wave is used to clean the wafer surface.
However, a portion of laser beam introduced with the laser induced plasma shock wave is directly introduced toward the wafer surface so that the wafer surface may be damaged.
Also the conventional laser induced plasma shock wave described above may be used to effectively remove inorganic dry particles but the laser induced plasma shock wave may not be used to remove organic contaminated particles and layers remained on the wafer surface.
Since, further, the laser induced plasma shock wave is generated in the air, the shock wave has a lower intensity and some elements such as oxygen within the air may be ionized to cause a surface damage, e.g., an oxidation, on the wafer surface.
It is, therefore, an object of the present invention to provide a dry surface cleaning apparatus using a laser from which both a first laser beam for generating a laser induced plasma shock wave to remove inorganic surface contaminants and a second laser beam for effectively removing organic surface contaminants may be generated so that organic and inorganic surface contaminants on the wafer surface may be effectively removed.
It is, therefore, another object of the present invention to provide an apparatus for changing the direction of a laser beam which could cause a damage to a wafer surface so that the laser beam may not be illuminated on the wafer surface and, therefore, the surface damage on the wafer surface may be basically prevented.
It is, therefore, still another object of the present invention to provide a dry surface cleaning apparatus with a beam expander and a laser nozzle to increase the intensity of the laser beam, to prevent the wafer surface from being damaged by a chemical reaction and to effectively remove surface contaminants.
In accordance with a preferred embodiment of the present invention, there is provided a dry surface cleaning apparatus for removing surface contaminants on a surface of a workpiece comprising:
a laser for generating a laser beam;
a beam delivery control unit for splitting the laser beam into a first and a second laser beam, wherein the first and the second laser beam propagate along different directions from each other;
a frequency modulator for modulating the second laser beam to generate a shorter wavelength laser beam, wherein the shorter wavelength laser beam has a shorter wavelength than that of the second laser beam and the shorter wavelength laser beam is used to directly detach the surface contaminants on the surface; and
a laser focusing lens for converging the first laser beam on a laser focus around the surface of the workpiece to generate a plasma shock wave around the laser focus, wherein the plasma shock wave is used to clean the surface contaminants on the surface.